Dimmers are generally used to regulate the illumination level output by a light source, e.g. a lamp or LED, by controlling the voltage, current, and/or power provided. Common dimming control solutions typically utilize either a 0-10V dimming, which provides a 0-10V direct current (DC) dim control signal to a power supply for the light source, or alternating current (AC) phase control, which varies the duty cycle of AC power supplied to a lighting device to provide a modified AC power signal. The lighting device receiving the modified AC power signal may be the light source directly, or a power supply providing regulated power to the light source. Commercial lighting applications requiring dimming most commonly use the 0-10V dimming control, while residential lighting most commonly uses AC phase control dimming. This disclosure relates to AC phase control dimming applications, particularly ensuring proper AC phase control mode compatible with the lighting device coupled to the phase dimmer, including adaptors for converting 0-10V dimming signals to control AC phase controlled lighting devices, and particularly to phase dimming applications associated with wireless lighting control systems.
AC phase control dimming, also commonly referred to as phase-cut dimming or simply—phase dimming, utilizes an power switching circuit, typically including a TRIAC, an SCR, or a pair of MOSFETs, to control the duty cycle of the AC power provided to the lighting device. Maximum power is provided to the light if the power switching circuit connecting the load to the power source is conducting on at all times, i.e., the switches conduct AC power throughout the entire phase or sinusoidal cycle of AC power. In this way the, the total available energy of the power source is transferred to the load.
To provide dimming, reduced power is provided to the lighting device by turning the switches off for a portion of each sinusoidal half-cycle (both positive and negative), thereby cutting off power to the lighting device for a portion of each half-cycle. A proportional amount of the power provided by each AC half-cycle is thereby effectively isolated from the lighting device, reducing the average energy provided to the lighting device, and dimming the light source. For example, if the switching circuit conducting each AC half-cycle is turned on or off half way through each AC half-cycle, then only one-half of the power will be transferred to the load, i.e. either the first half or the second half of each half-cycle. By adjusting the point in each phase half-cycle at which the power switching circuit either begins to conduct or stops conducting the AC power to the load, the overall effect in the case of a light source will be a smooth dimming action resulting in the control of the luminosity of the light source from off to fully on.
In some applications the phase-cut power signal is provided directly to the lamp. This is most commonly the case with incandescent lamps. In many other applications, the phase-cut power signal provides power to a power supply from which the lamp is powered. Type of lighting power supplies include ballasts, drivers, Electronic Low Voltage (ELV), and Magnetic Low Voltage (MLV). Phase dimming is available using more than one mode of phase-cut operation. The mode best suited for the application depends on the type of lighting device being powered and its compatibility with that particular mode.
Reverse Phase or Trailing Edge dimming is a phase dimming mode in which each half-cycle begins with the switching circuit conducting power to the lighting device and then the switching circuit is turned off, the phase is ‘cut,’ later in the half-cycle. Forward Phase or Leading Edge dimming is a phase dimming mode in which each half cycle begins with the switching circuit turned off and then the switch is turned on later in the half-cycle, providing power to the lighting device in the remaining portion of each half-cycle. Depending on the electrical characteristics of the type of load, one phase dimming mode may be preferred over the other.
For resistive loads, voltage and current remain in phase. For capacitive loads, voltage lags current. And for an inductive loads, current lags voltage. Incandescent lamps are generally a resistive load, and while either phase dimming mode works for resistive loads because voltage and current remain in phase, Reverse Phase dimming is typically preferred. ELV power supplies and power supplies for Compact Florescent Lamps (CFL) typically use solid state electronic switching and are generally a capacitive load best suited for Reverse Phase dimming in which power is conducted at the beginning of each half-cycle and to dim, the switching circuit cuts-off power conduction at some point in the half-cycle. Capacitive loads induce an inrush current spike when power is connected, so turning the switch on to provide power when voltage is crossing through zero minimizes the effect of such transient electrical characteristics upon the start of conduction by limiting the power available during the transient.
In contrast, MLV power supplies use a magnetic transformer and thus are an inductive load best suited for Forward Phase dimming in which power is cut-off at the end of each half-cycle, and the switching circuit turns power on at some point at or subsequent to the beginning of the half-cycle, depending on the desired dimming level. Inductive loads induce a voltage spike or “fly-back” and associated ringing when power is disconnected, so turning the switching circuit off when voltage is crossing through zero minimizes the effect of this transient electrical characteristics as compared to the characteristics of a fly-back occurring at a higher power transfer point in the AC half-cycle.
Some ringing may occur with an MLV load using either Reverse Phase or Forward Phase dimming; however, when an MLV power supply is used with Forward Phase dimming, the ringing and associated effects are minimized. Negative effects relating to inductive fly-back and ringing if the nonpreferred Reverse Phase dimming is used with an MLV power supply include instability leading to audible noise, over heating from high peak currents, visible lighting effects such as flicker, shimmer, or ripple, and dead travel over a range of dimmer adjustment.
Phase dimmers are typically available in at least three types: (1) dimmers having only one of the above modes of phase dimming; (2) dimmers provide a manually selectable mode of phase dimming; and (3) dimmers providing automatic detection of the type of load and setting of the preferred mode of phase dimming for that type of load. If the type of phase dimming to be used for a load is set by selecting a dimmer using the preferred mode of the dimmer for a load or by manually selecting the mode for a manually selectable phase dimmer, the mode of phase dimming required may be mistakenly mismatched for the given type of load connected during installation, resulting in faulty or unreliable dimming operation, including the negative effects discussed above. Therefore, a phase dimmer capable of automatically detecting load type and setting the preferred mode for the connected load is preferable.
Several prior art phase dimming solutions provide automatic load-type detection and automatic phase-mode setting, with each providing a different technical solution to the problem. Common to the prior solutions is that each seeks to detect undesirable electrical characteristics of an inductive load connected to the phase dimmer and to set the phase dimming mode accordingly.
Some prior art phase dimmers include a high pass filter to extract a ringing portion of the load signal subsequent to the switching off of AC power to the load. These prior art phase dimmers then either capture and hold the peak of the ringing signal for comparison to a reference threshold, or digitally sample and study various characteristics of the ringing signal to determine if it is indicative of an inductive load. If the captured peak exceeds a reference threshold, then the load is determined to be inductive and the Forward Phase dimming mode is selected. Another prior art solution uses power phase monitoring to determine the phase relationship of current and voltage when powering the load to determine if the current phase lags the voltage phase, indicating the likelihood of an inductive load. Yet another prior art solution requires a different switching circuit shut-off transient time for initial load-type detection than is used for ongoing dimming operation. Similarly, another one of the prior art solutions requires a particular dimming setting be used for load-type detection and yet another prior art solution requires a specially dimming profile be executed during load-type detection.
Various disadvantages are associated with the prior art phase dimming solutions for automatic load-type detection and phase-mode setting. In particular, each of these prior art solutions require complex, costly circuits that are typically used only for the purpose of load-type detection, then are not subsequently used for operation. Additionally, some of these prior art solutions are relatively slow, for example, requiring up to 500 milliseconds to reasonably reliably determine the load-type connected to the dimmer. Furthermore, some of these prior art solutions are susceptible to false positive detections of an inductive load. For example, when the peak of a transient signal is the only parameter measured, such a transient spike detected may be an artifact of something other than the load-type being inductive, which may produce a false positive from such a transient condition, including, for example, from AC line noise. Additionally, other load types other than inductive loads can produce switch-off ringing under particular circumstances or combinations, which may produce a false positive when the presence of a ringing signal is alone used to determine load-type.
As such, it was realized by the inventors of the current disclosure that improvements are needed to reliably and economically provide automatic load-type detection and phase-cut mode selection for lighting devices, including for phase-cut dimmers and for 0-10 V to phase-cut adaptors, and as used in wireless lighting control system applications.